Generally, an electric vehicle has such a configuration that the electric vehicle takes in power from an overhead wire by a power collector, uses the power taken therein to drive a motor by an electric power conversion system such as an inverter to run.
In the electric vehicle, at the time of braking the vehicle, a so-called regenerative brake that acquires a braking force by causing a motor to perform a regenerative operation is used. The regenerative power generated at this time is supplied to other power running vehicles present near the vehicle itself or to the load such as an air conditioning system of the vehicle via the overhead wire or the third rail and consumed therein.
However, at early morning, during night, or in unbusy lines in which the number of trains operated is less, another vehicle may not be present near the vehicle itself (the regenerative load may be insufficient), and thus the regenerative power generated by the regenerative brake may not be consumed sufficiently. If the regenerative power of the vehicle itself increases than the power consumed by other vehicles, a trolley voltage increases, thereby tripping various devices connected to the overhead wire due to overvoltage or causing a damage.
Therefore, when the trolley voltage has increased, the inverter device narrows down the regenerative brake and performs regenerative narrowing-down control to suppress generation of the regenerative power. At this time, because the regenerative braking force decreases due to the regenerative narrowing-down control, the braking force, which has decreased and becomes insufficient, is compensated by a friction brake.
On the other hand, use of the friction brake leads to disposal of a part of kinetic energy of the electric vehicle that can essentially regenerate power to the air as heat, which is not desirable from a viewpoint of energy saving.
Therefore, such a system has been developed that a power storage element such as a secondary battery or an electric double layer capacitor is mounted on an electric vehicle, to store regenerative power in the power storage element as required, thereby acquiring a stable regenerative brake even if the regenerative load is insufficient.
Furthermore, when the electric vehicle performs power running, the electric vehicle can run while appropriately controlling allocation of electric power supplied from the overhead wire and electric power discharged from the power storage element, which becomes energy saving.
Further, when an electric vehicle mounted with the power storage element runs in a non-electrified section in which reception of electric power from the overhead wire is not performed, only the power from the power storage element is used to drive and accelerate the motor, and all the regenerative power generated by the motor at the time of braking is stored in the power storage element (see, for example, Patent Literature 1).